Reference interval of TSH in the first trimester of pregnancy and its relationship to further thyroid examinations

Drahomira Springer1,2

Introduction: Determining TSH in the serum is a basic test for the diagnosis of thyroid function in the general population. Its regulation is based on feedback, however during pregnancy there are other mechanisms  mainly suppression of TSH due to a high hCG and the iodine saturation.

Aim: Results of TSH, anti TPOAb and FT4 by ADVIA Centaur (Siemens) in our group of 7530 women living in iodine sufficient area in 911 week of pregnancy were determined. For evaluation of the reference intervals for pregnant women was calculated from selected group in accordance with the recommendations of the NACB. A reference interval for TSH in the first trimester of pregnancy was determined as 0.063.67 mU/l. Determination of anti-TPOAb in pregnancy is diagnostically and prognostic important. The limit for anti-TPOAb positive was determined to be 143 kU/l. Higher TSH is also very often associated with positivity of anti-TPO antibodies. In the group with TSH>3.67 mU/l there were 44.1% of women with antibody positivity. The relationship to ultrasound results will be presented.

The average level of hCG in the group of pregnant women with suppressed TSH was almost double (Mean=95.6 mg/ml) in comparison with the group with TSH in reference interval (Mean=68.9 mg/ml).

Conclusion: The pivotal importance of each laboratory test (TSH, TPOAb, FT4 and thyroid ultrasound) and the necessity of reference interval for each method in the study region for early diagnosis of thyroid disease in pregnancy is emphasized.